The deterioration of bridges has been acknowledged as a critical safety problem in our Nation's transportation system. The rehabilitation and redecking of existing deficient structures, as well as designs for new structures, must cope with many factors affecting bridge construction and rehabilitation. These factors include increased usage, increased loading, reduced maintenance, and the need for lower costs, lighter weight, and more efficient construction techniques. The available deck systems heretofore used all have specific beneficial characteristics, but none have all of the features required to meet current needs.
Both open grid and filled grid decks are known and commonly used. Filled grating or grid allows concrete or similar material to fill or partially fill the interstices of the grating or grid. This results in an extremely heavy modular panel which is unwieldy and costly to construct and imposes undesirable dead load which serves no useful purpose in bridge deck construction. Open grating bridge decks without a concrete or similar filling are unacceptable for most situations because they are considered too dangerous to vehicular traffic and also dangerously allow objects to fall through the open grid surface.
U.S. Pat. Nos. 4,531,857 and 4,531,859 disclose a revolutionary new design for decks which has met all the above design factors. These patents disclose a prefabricated pavement module for bridges and the like and a method of making the module. The module includes a base grating and a concrete overlay. Studs are attached to the grating and extend into the concrete overlay. The studs transfer horizontal shear and provide a composite interaction between the grating and overlay. These grid decks are commonly known as exodermic decks.
An exodermic deck has section properties increased by 150% to 300% over that of known conventional grid deck constructions. An exodermic deck eliminates potential fatigue failure thereby providing a higher load capacity and extending the useful life of the existing grid deck. The exodermic deck relocates the neutral axis of the composite deck and reduces the maximum stress level in the top surface of the grid to a point at which fatigue failure should not occur. The exodermic deck system also eliminates the need for constant repair of broken grid bars and connections which is common with open grid deck installations. Moreover, an exodermic deck eliminates skidding and noise problems commonly associated with open grid deck bridges and with filled grid deck bridges which do not have a wearing surface above the grid. It is also significantly lighter than known filled or partially filled grid decks, which is highly desirable in bridge construction.
Exodermic decks are revolutionizing the bridge building industry. Exodermic decks may be used to replace worn out or damaged decks as well as to construct new bridges. In some instances, however, an existing grid deck is not worn out or damaged, but there is still a need or desire to convert the existing deck to an exodermic deck to realize the improved load capacity, wear life, and other benefits of an exodermic deck. Therefore, the problem exists of converting an existing filled, partially filled, or open grating grid deck, having a grating which is still useable, to an exodermic deck.